Chapter 7 Community Ecology.

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2 Chapter Overview QuestionsWhat determines the number of species in a community?How can we classify species according to their roles in a community?How do species interact with one another?How do communities respond to changes in environmental conditions?Does high species biodiversity increase the stability and sustainability of a community?

3 Core Case Study: Why Should We Care about the American Alligator?Hunters wiped out population to the point of near extinction.Alligators have important ecological role.Figure 7-1

4 Core Case Study: Why Should We Care about the American Alligator?Dig deep depressions (gator holes).Hold water during dry spells, serve as refuges for aquatic life.Build nesting mounds.provide nesting and feeding sites for birds.Keeps areas of open water free of vegetation.Alligators are a keystone species:Help maintain the structure and function of the communities where it is found.

5 COMMUNITY STRUCTURE AND SPECIES DIVERSITYBiological communities differ in their structure and physical appearance.Figure 7-2

6 Species Diversity and Niche Structure: Different Species Playing Different RolesBiological communities differ in the types and numbers of species they contain and the ecological roles those species play.

7 Species Diversity and Niche StructureNiche structure: how many potential ecological niches occur, how they resemble or differ, and how the species occupying different niches interact.Geographic location: species diversity is highest in the tropics and declines as we move from the equator toward the poles.

8 TYPES OF SPECIESNative, nonnative, indicator, keystone, and foundation species play different ecological roles in communities.Native: those that normally live and thrive in a particular community.Nonnative species: those that migrate, deliberately or accidentally introduced into a community.

9 Case Study: Species Diversity on IslandsMacArthur and Wilson proposed the species equilibrium model or theory of island biogeography in the 1960’s.Model projects that at some point the rates of immigration and extinction should reach an equilibrium based on:Island sizeDistance to nearest mainland

10 Indicator Species: Biological Smoke AlarmsSpecies that serve as early warnings of damage to a community or an ecosystem.Presence or absence of trout species because they are sensitive to temperature and oxygen levels.

11 Case Study: Why are Amphibians Vanishing?Frogs serve as indicator species because different parts of their life cycles can be easily disturbed.Figure 7-3

13 SPECIES INTERACTIONS: COMPETITION AND PREDATIONSpecies can interact through competition, predation, parasitism, mutualism, and commensalism.Some species evolve adaptations that allow them to reduce or avoid competition for resources with other species (resource partitioning).

14 Resource PartitioningEach species minimizes competition with the others for food by spending at least half its feeding time in a distinct portion of the spruce tree and by consuming somewhat different insect species.Figure 7-7

16 SPECIES INTERACTIONS: COMPETITION AND PREDATIONSpecies called predators feed on other species called prey.Organisms use their senses their senses to locate objects and prey and to attract pollinators and mates.Some predators are fast enough to catch their prey, some hide and lie in wait, and some inject chemicals to paralyze their prey.

17 PREDATIONSome prey escape their predators or have outer protection, some are camouflaged, and some use chemicals to repel predators.Figure 7-8

18 SPECIES INTERACTIONS: PARASITISM, MUTUALISM, AND COMMENSALIMParasitism occurs when one species feeds on part of another organism.In mutualism, two species interact in a way that benefits both.Commensalism is an interaction that benefits one species but has little, if any, effect on the other species.

19 Parasites: Sponging Off of OthersAlthough parasites can harm their hosts, they can promote community biodiversity.Some parasites live in host (micororganisms, tapeworms).Some parasites live outside host (fleas, ticks, mistletoe plants, sea lampreys).Some have little contact with host (dump-nesting birds like cowbirds, some duck species)

20 Mutualism: Win-Win RelationshipTwo species can interact in ways that benefit both of them.Figure 7-9

21 Commensalism: Using without HarmingSome species interact in a way that helps one species but has little or no effect on the other.Figure 7-10

22 ECOLOGICAL STABILITY AND SUSTAINABILITYLiving systems maintain some degree of stability through constant change in response to environmental conditions through:Inertia (persistence): the ability of a living system to resist being disturbed or altered.Constancy: the ability of a living system to keep its numbers within the limits imposed by available resources.Resilience: the ability of a living system to bounce back and repair damage after (a not too drastic) disturbance.

23 ECOLOGICAL STABILITY AND SUSTAINABILITYHaving many different species appears to increase the sustainability of many communities.Human activities are disrupting ecosystem services that support and sustain all life and all economies.